This invention relates to manual feedback control systems and, in particular, to systems in which the feedback to an operator is obtained either partially or entirely from a model of the desired system response. While the invention is described with particular emphasis in association with aircraft steering control using visual feedback to the operator, those skilled in the manual control art will recognize the wide applicability of our invention to other manual control feedback systems.
The task of precisely steering modern aircraft, particularly high performance aircraft, has become increasingly difficult. The inherent delay between the time that a pilot performs a control action and the time that he can perceive its effect is such that only highly skilled and expertly trained pilots can avoid the tendency to over control the aircraft, thereby causing pilot-induced oscillations. Moreover, some steering displays are computed from measured aircraft variables such as rotational rates or accelerations. During oscillatory control periods, the oscillations can be reflected into the steering display which further aggravates the problem through regenerative feedback action. The invention disclosed hereinafter was the result of an investigation to determine the efficacy of idealized visual feedback on the problem of pilot steering control. In particular, the invention was initially conceived in an effort to improve and simplify the steering associated with air-to-air gun fire control.
The prior art approach to aircraft gun fire control (gunsight) systems and their associated displays has been based upon the use of actual measured data for steering computations. This has often resulted in display systems which exhibit the regenerative feedback action mentioned previously when aircraft rotational rates or accelerations are used. Gunsights whose displays exhibit this phenomenon are commonly referred to as "disturbed" systems. One means for alleviating the steering difficulties caused by "disturbed" gunsight systems is to utilize autonomous, stabilized target tracking devices, such as radar, electro-optical, or infrared tracking systems. Such gunsight systems (commonly referred to as "director" systems) provide measurement and corresponding displayed data which are relatively immune to the disturbing effect of aircraft motion and show a correspondingly higher performance capability during precision steering. However, director systems are costly, increase aircraft weight and space requirements, and generally fail to make maximum use of the visual tracking capability of the pilot. The invention disclosed hereinafter is intended to provide improved aircraft steering, comparable to that obtainable through the use of director gunsight systems, without the need for sophisticated autonomous tracking devices. By thus improving and making use of the tracking capability of the pilot, the invention permits the implementation of a director-type gunsight, that is, one having improved steering dynamics characteristics, without the attendant disadvantages of present director systems. The invention is further intended for use in conjunction with presently available aircraft avionics systems. In particular, the invention makes use of modern display devices which provide electronically generated images on a combining glass such that the steering display or indicator is superimposed on the pilot's forward field of view. Such displays are commonly referred to as heads-up displays and the electronic display device is called a HUD (Heads-Up-Display).
An essential feature of our invention is that displayed information is referenced not to the actual aircraft but to a model of the desired behavior of the aircraft. This provides timely and effective feedback to the pilot and promotes smooth steering. Pilot control actions are converted to signals that feed both the actual aircraft and the model or command aircraft. The actual and command aircrafts exhibit brief behavioral differences, but are driven toward coincidence, for example, either by slowly driving the command aircraft orientation to that of the actual aircraft through display means, or by driving the actual aircraft into coincidence with the command aircraft through the flight control system.
Our invention has a wide range of applications. For example, it may be used in conjunction with airborne trainable gun application in which the gun, over its degrees of freedom, is slaved to the command aircraft rather than being fixed to the actual aircraft. Also, it may be used for precise velocity vector control in tasks such as air-to-ground bombing, terrain following, or landing. In its broader aspects, it may find application in a variety of manual control systems where the inherent reaction time, control sensitivity, and inaccessibility of pertinent measurement data cause the operator difficulty in accomplishing his control task.
One of the objects of this invention is to provide an improved aircraft steering system.
Another object of this invention is to provide a low-cost aircraft steering system.
Another object of this invention is to provide a novel method of manually controlling a system by observing the effect of the control action on a model of the system using sensory feedback.
Yet another object of this invention is to provide a fire control system for aircraft which displays information to the pilot of the aircraft in terms of a model of the aircraft.
Yet another object of this invention is to provide a method for simplifying the steering task of a pilot.
Still another object of this invention is to provide an improved method to permit terrain followed by an aircraft.
Yet another object of this invention is to provide an improved system for use in automatic ground control approach systems for aircraft.
Still another object of this invention is to provide an aircraft steering system suitable for use in trainable gun applications.
Yet another object of this invention is to provide a steering control apparatus for use in conjunction with aircraft flight control systems having a multi-mode operational characteristic.
Another object of this invention is to provide a low-data-rate means for providing remote steering of nonpiloted aircraft.
Other objects of this invention will be apparent to those skilled in the art in light of the following description and accompanying drawings.